\documentclass[12pt,a4paper]{report}
\begin{document}
\begin{equation}
\left(
\left[
\left\{
\sqrt{
a+b
}
\right\}
\right]
\right)
\end{equation}

\ifnum\x<1
\left[
\left\{
\sqrt{
a+b
}
\right\}
\right]
\fi

\left[
\ifnum\x<1
\left\{
\sqrt{
a+b
}
\right\}
\fi
\right]

\left[
\begin{one}
\left\{
\sqrt{
a+b
}
\right\}
\end{one}
\right]
\end{document}
